The present invention relates to stabilization systems and in particular to systems for stabilizing sensitive, vehicle-borne apparatus from uncontrolled and unwanted motions of the vehicle, such as vibrations and shocks in both translational and rotational types of motion.
The problem of stabilizing apparatus mounted on a moving vehicle is one to which considerable effort has been applied. Most prior art systems have been designed for use with inertial platforms and as a result they stabilize against relatively low frequency or relatively high frequency movements, but not both.
Prior art stabilized camera mounts such as described in the patent to D. E. Moors, et al., U.S. Pat. No. 3,094,054, issued to the assignee of the present invention of June 18, 1963, tend to isolate the camera from a fairly complete spectrum of frequencies, but at the expense of substantial complexity. A three-axis, flexure gimbal system upon which the camera was mounted stabilized the camera against angular motion. The camera was movable about any of the three axis by appropriate torquer solenoids.
It is desirable that a stabilization system intended to isolate sensitive equipment such as a camera should operate over a wide frequency range, including frequencies as low as 0.01 Hz. Hz. The stabilization system should not have any resonating members, since these will tend to amplify vibrational inputs. It is further desirable that a stabilization system be of reasonable size, light in weight, reliable, and efficient in the use of electrical power. The system should be fail-safe in the event of power failures to avoid damage to the sensitive apparatus.
Very low frequencies, below 1 Hz can generally be attenuated by gyro-controlled gimbal platforms that reject angular motion. Most inertial platforms are very effective in this spectral region. Higher frequencies, greater than 100 Hz are usually attenuated by conventional vibration mounts whose resonance frequencies are generally in the range of 5 to 50 Hz.
Thus, it is the middle range of frequencies, from 1 to 100 Hz that the major isolation problem exists. The prior art approach to that problem, represented by the above-mentioned patent to Moors, et al., makes use of a system in gimbal rings, vibration mounts, and rate gyros.
A more recent approach is described in the patent to E. L. Forys, et al, entitled "Wide Band Stabilizer," U.S. Pat. No. 3,703,999, issued to the assignee of the present invention on Nov. 28, 1972. The apparatus to be stabilized was mounted on soft spring isolators. Torque-cancelling signals were applied to linear actuators in parallel with the soft spring isolators. Servo circuitry derived appropriate torque-cancelling signals from rate gyros and angular accelerometers.
This system operates well over a very broad frequency spectrum. Low frequencies are attenuated by an active servo loop utilizing a rate gyro. Intermediate frequencies are attenuated by the angular accelerometer servo loop. The higher frequencies are attenuated by the compliance of the soft spring isolators. Because the angular motion capability of the system is limited, some applications might require that the sensitive apparatus or a part of it be gimbal mounted in the stabilized package.
The present invention is distinguishable from the above mentioned Wide Band Stabilizer described in U.S. Pat. No. 3,703,999. Where Forys, et al. stabilized and supported the sensitive apparatus from the vehicle structure by a parallel combination of a soft spring isolator and a linear actuator, the present invention isolates the apparatus to be stabilized from the vehicle structure by use of a linear actuator in parallel with the series combination of a bearing and a complaint isolator. In different embodiments the bearing may be either a conventional rolling or sliding frictional bearing or it may be a torsional pivot, the latter having no friction but having a restoring torque proportional to angular displacement.
According to the preferred embodiment of the present invention, the apparatus is supported at its center of gravity in three degrees of rotational freedom. Linear actuators are connected directly to the sensitive apparatus, and are capable of applying wideband counter-rotational forces directly to the sensitive apparatus in response to rotational inputs. This permits the actuator to be effective against the coupled torques which result from unavoidable residual displacement of the center of gravity of the sensitive apparatus from the kinematic center of the bearing.